Damaged proteins and their aggregated products are formed during oxidative stress and aging. 26S proteasomes can recognize and remove these damaged and unfolded proteins; moreover, decreased function of the ubiquitin-proteasome system is associated with the development of age-related degenerative diseases. It is our hypothesis that maintenance or enhancement of ubiquitin-proteasome function is a novel strategy to prevent or attenuate these age-related diseases. Our preliminary results indicate that dithiolethiones, which protect against the toxicities of environmental agents by stimulating expression of the downstream genes of the Nrf2 signaling pathway, increase expression of multiple subunits of 26S proteasomes and ubiquitinating enzymes in mouse liver. This proposal is designed to a) evaluate the physiological benefit of induced proteasome expression in cells following challenge by toxicants, b) determine the impact of inducible proteasome expression and the role of Nrf2 on the accumulation of damaged proteins in young and senescence murine fibroblasts as a model of aging, c) characterize inducible patterns and levels of proteasome expression in murine tissues, especially in the brain, following dithiolethione-treatment. Functional effects of enhanced proteasome induction will be initially investigated in cultured cells using murine embryonic fibroblasts and neuroblastoma cells. Measures of proteasome levels, proteolytic activities, protein turnover rates and accumulation of damaged proteins following chemical challenge will be compared in cell models in which proteasome expression is elevated by pharmacological intervention and through molecular genetic expression of specific proteasome subunits. The role of Nrf2 in these protective effects will be examined using nrf2-disrupted or inhibited cells as well as by comparisons in wild-type and nrf2-deficient mice of different ages. Collectively, these studies will explore the possible protective role of enhanced proteasome expression against exogenous toxic chemicals and degenerative processes that accompany aging. The long-term goal of this project is to rigorously evaluate the concept that increased expression of ubiquitin-proteasomes pathway through activation of the Nrf2 signaling cascade can prevent or retard the progression of human degenerative diseases such as Alzheimer's, Parkinson's disease and amyotrophic lateral sclerosis.